The preferred credential is applicable for domain user.
To mark as preferred credential:
On the admin home page, select Shared Credentials.
The Shared Credentials screen is displayed.
Select Mark as Preferred Credential
icon on a shared credential.
Select Confirm to add your endpoint as preferred machine on the displayed pop-up box.
The shared credential is marked as preferred machine successfully.
Note: To remove shared credential as the preferred machine, you can unstar them.